5. NET INCOME PER SHARE

On May 1, 2013, pursuant to the Second Modified Fifth Amended Plan of Reorganization of Ambac (the "Reorganization Plan"), 45,000,000 shares of new common stock at par value of $0.01 per share and 5,047,138 warrants were issued. Warrants entitled such holders to acquire up to 5,047,138 shares of new common stock at an exercise price of $16.67 per share at any time on or prior to April 30, 2023. For the years ended December 31, 2017, 2016 and 2015, 0, 136, and 740, warrants, respectively, were exercised, resulting in an issuance of 0, 136 and 236 shares of common stock.

On June 30, 2015, the Board of Directors of Ambac authorized the establishment of a warrant repurchase program that permits the repurchase of up to $10,000 of warrants. On November 3, 2016, the Board of Directors of Ambac authorized a $10,000 increase to the warrant repurchase program. For the year ended December 31, 2017, Ambac repurchased 0 warrants at a cost of $0. As of December 31, 2017, Ambac had repurchased 985,331 warrants at a cost of $8,092, (average cost of $8.21 per warrant), leaving 4,053,670 warrants outstanding. The remaining aggregate authorization at December 31, 2017 is $11,939.

The following table provides a reconciliation of the common shares used for basic net income per share to the diluted shares used for diluted net income per share:



Year Ended December 31,	2017	2016	2015
Basic weighted average shares outstanding	45,367,932	45,212,414	45,173,542
Effect of potential dilutive shares⁽¹⁾:
Warrants	—	312,619	809,834
Stock options	—	447	5,313
Restricted stock units	—	116,105	14,221
Performance stock units	—	81,939	3,117
Diluted weighted average shares outstanding	45,367,932	45,723,524	46,006,027
Anti-dilutive shares excluded from the above reconciliation
Stock options	126,667	110,000	110,000
Warrants	4,053,670	—	—
Restricted stock units	68,654	—	—
Performance stock units ⁽²⁾	322,943	—	—


(1)	For the year ended December 31, 2017, Ambac has a net loss and accordingly excluded all potentially dilutive securities from the determination of diluted loss per share as their impact was anti-dilutive.


(2)	Performance stock units are reflected herein at their target issuance amounts. Vesting of these units is contingent upon meeting certain performance metrics. Although a portion of these performance metrics have been achieved as of the respective period end, it is possible that awards may no longer meet the metric at the end of the performance period.